Rankine cycle apparatus have been known as systems for converting heat energy into mechanical work. The Rankine cycle apparatus include a structure for circulating water as a working medium, in the liquid- and gaseous-phase states within a sealed piping system forming a circulation system in the apparatus. Generally, the Rankine cycle apparatus include a water supplying pump unit, an evaporator, an expander, a condenser, and pipes connecting between these components to provide circulation circuitry.
FIG. 17 hereof is a schematic block diagram of a general setup of a conventionally-known Rankine cycle apparatus (e.g., vehicle-mounted Rankine cycle apparatus) and certain details of a condenser employed in the Rankine cycle apparatus. The Rankine cycle apparatus of FIG. 17 includes a water supplying pump unit 110, an evaporator 111, an expander 107, and the condenser 100. These components 110, 111, 107 and 100 are connected via pipes 108 and 115, to provide circulation circuitry in the apparatus.
Water (liquid-phase working medium), which is supplied, a predetermined amount per minute, by the water supplying pump unit 110 via the pipe 115, is imparted with heat by the evaporator 111 to turn into water vapor (gaseous-phase working medium). The vapor is delivered through the next pipe 115 to the expander 107 that expands the water vapor. Mechanical device (not shown) is driven through the vapor expansion by the expander 107 so as to perform desired mechanical work.
Then, the expanded water vapor is delivered through the pipe 108 to the condenser 100, where the vapor is converted from the vapor phase back to the water phase. After that, the water is returned through the pipe 115 to the water supplying pump unit 110, from which the water is supplied again for repetition of the above actions. The evaporator 111 is constructed to receive heat from an exhaust pipe extending from the exhaust port of the engine of the vehicle. Among various literatures and documents showing structural examples of the Rankine cycle apparatus is Japanese Patent Application Laid-open Publication No. 2002-115504.
The following paragraphs detail a structure and behavior of the condenser 100 in the conventional vehicle-mounted Rankine cycle apparatus, with reference to FIGS. 17 to 19.
The condenser 100 includes a vapor introducing chamber 101, a water collecting chamber 102, and a multiplicity of cooling pipes 103 vertically interconnecting the two chambers 101 and 102. In FIG. 17, only one of the cooling pipes 103 is shown in an exaggerative manner. Substantial upper half of the interior of each of the cooling pipes 103 is a vapor (gaseous-phase) portion 104 (i.e., portion occupied with the vapor 104), while a substantial lower half of the interior of the cooling pipe 103 is a water (liquid-phase) portion 105 (i.e., portion occupied with the water 105). In the vapor (gaseous-phase) portion 104, most of the working medium introduced via the vapor introducing chamber 101 to the cooling pipe 103 is in the gaseous phase, while, in the water portion 105, most of the working medium flowing through the cooling pipe 103 is kept in the liquid (condensed water) phase. Boundary between the vapor 104 and the water 105 (i.e., gas-liquid interface) is a liquid level position 112.
One cooling fan 106 is disposed behind the cooling pipes 103 (to the right of the cooling pipes 103 in FIG. 17). The cooling fan 106 is surrounded by a cylindrical shroud 106a. Normally, operation of the cooling fan 106 is controlled by an electronic control unit on the basis of a water temperature at an outlet port of the condenser 100. The single cooling fan 106 sends air to the entire region, from top to bottom, of all of the cooling pipes 103 to simultaneously cool the cooling pipes 103.
The condenser 100 operates as follows during operation of the Rankine cycle apparatus. Water vapor of a relatively low temperature, discharged from the expander 107 with a reduced temperature and pressure, is sent into the vapor introducing chamber 101 of the condenser 100 via the low-pressure vapor pipe 108 and then directed into the cooling pipes 103. Cooling air 109 drawn into the cooling fan 106 is sent to the condenser 100.
Strong cooling air is applied by the cooling fan 106 to the upstream vapor portion 104 of the condenser 100, i.e. a portion of each of the cooling pipes 103 where a mixture of the vapor and water exists, and thus latent heat emitted when the vapor liquefies can be recovered effectively by the cooling air. Cooling air is also applied by the cooling fan 106 to the downstream water portion 105 of the condenser 100, i.e. a portion of each of the cooling pipes 103 where substantially only the water exists. Water condensed within the cooling pipes 103 of the condenser 100, is collected into the water collecting chamber 102 and then supplied by the water supplying pump unit 110 to the evaporator 111 in a pressurized condition as noted above.
In FIG. 17, reference numeral 116 represents a surface area of a condensing heat transmission portion, and 117 represents a surface area of a heat transmission portion of the condensed water. The surface areas 116 and 117 of the heat transmission portions and the liquid level position 112 have the following relationship.
The conventional Rankine cycle apparatus 100 inherently has the characteristic that the liquid fluid position 112 varies. Namely, because the engine output varies in response to traveling start/stop and transient traveling velocity variation of the vehicle, the amount of water supply to the evaporator 111 also varies, in response to which the liquid level position 112 within the condenser 100 varies. Namely, in the condenser 100, the liquid level position 112 rises when the amount of the vapor flowing into the condenser 100 (i.e., inflow amount of the vapor) is greater than the amount of the condensed water discharged from the condenser 100 (i.e., discharge amount of the condensed water), but lowers when the inflow amount of the vapor is smaller than the discharge amount of the condensed water. In this way, the vapor-occupied portion 104 in the cooling pipes 103 of the condenser 100 increases or decreases. Because the condensed water (in the portion 105) is discharged from the water supplying pump unit 110 subjected to predetermined flow rate control, a pressure from an outlet port 113 of the expander 107 to an inlet port 114 of the water supplying pump unit 110 is determined by a pressure within the condenser 100. The pressure within the condenser 100 is determined by an amount of condensing heat exchange caused by cooling of the vapor portion 104 of the condenser, and the amount of condensing heat exchange is determined by a flow rate of the medium to be cooled and a surface area of the condensing heat transmission portion 116. Thus, if the portion occupied with the vapor increases or decreases due to variation (rise or fall) of the liquid level position 112, the surface area 116 of the condensing heat transmission portion increases or decreases and so the pressure within the condenser 100 and the flow rate of the medium to be cooled do not uniformly correspond to each other any longer.
Similarly, the temperature of the condensed water at the outlet port of the condenser 100 is determined by an amount of heat exchange caused by cooling of the water portion 105 of the condenser, and the amount of the heat exchange of the condensed water is determined by the flow rate of the medium to be cooled and a surface area 117 of a heat transmission portion of the condensed water. Thus, if the portion occupied with the condensed water 105 increases or decreases due to variation (rise or fall) of the liquid level position 112, the surface area 117 of the heat transmission of the condensed water portion increases or decreases and so the temperature of the condensed water and the flow rate of the medium to be cooled do not uniformly correspond to each other any longer.
In the Rankine cycle apparatus where water is used as the working medium, the saturation pressure, at an atmospheric temperature, of the water within the circulation system is lower than the atmospheric pressure, and so the interior of the circulation system would assume a negative pressure after deactivation of the Rankine cycle apparatus as the entire apparatus is cooled. Thus, a non-condensing (i.e., non-condensable) gas, such as air, would enter the interior of the circulation system through sealed portions of various components and joints between the pipes. Further, where the working medium used has a saturation pressure at an atmospheric temperature greater than the atmospheric pressure, and if the working medium is contained in the circulation system in poor filling condition, the non-condensing gas, such as air, would remain within the circulation system of the apparatus.
If the Rankine cycle apparatus is operated with the non-condensing gas present or contained within the circulation system of the Rankine cycle apparatus, the non-condensing gas would enter the condenser 100 along with a flow of vapor. In such a case, the vapor 104 having entered the condenser 100 condenses within the condenser 100 and is discharged as condensed water 105, as illustrated in FIG. 18. On the other hand, the non-condensing gas 121, having flown into the condenser 100, would build up or accumulate within the condenser 100 due to its con-condensable characteristic. Because the flow of the vapor 104 from the expander 107 to the condenser 100 is present in an upstream region of the condenser 100, the non-condensing gas 121 is carried, by the flow of the vapor 104, to a lower area of the vapor portion 104 within the condenser 100. In other words, the circulation system is formed systematically, in the Rankine cycle apparatus, by the flows of the water and vapor as illustrated in FIG. 17, and the non-condensing gas too flows into the circulation system in accordance with the flow of the vapor 104 through the pipe 108 extending from the expander 107 to the condenser 100.
The condensable vapor 104 condenses by the condensing operation of the condenser 100 and is discharged from the condenser 100 as condensed water 105. The non-condensing gas, on the other hand, does not condense and would therefore remain within the condenser 100 in the gaseous-phase state while being subjected to the vapor flow. As a consequence, the non-condensing gas would remain in the lower area of the vapor portion 104 within the condenser 100 as denoted at 121 in FIGS. 18 and 19.
Further, because the interior of the condenser 100 is placed in conditions such that the air density is greater than the vapor density, air would accumulate in the lower area of the vapor portion 104 due to the action of gravity. Actually, in the boundary between the gaseous-phase portion 118 (corresponding to the vapor portion 104) and the liquid-phase portion 119 (corresponding to the water portion 105), there would be produced water and condensate liquid membrane 105a as illustrated in FIG. 19. The non-condensing gas 121 is surrounded by the water 105 and condensate liquid membrane 105a and pressed in an upstream-to-downstream direction by the flow of saturated vapor 104. As a consequence, the non-condensing gas (i.e., air) 121 having a greater density than the vapor 104 would be accumulated in the lower area of the gaseous-phase portion (i.e., condensing heat trans-mission portion) within the condenser 100. Thus, in the lower area of the gaseous-phase portion within the condenser 100, as illustrated in FIGS. 18 and 19, the non-condensing gas 121 would become a resistance to impede passage of the saturated vapor 104 supplied from upstream, and so there would be formed an area 122 where the saturated vapor 104 can never reach or can only reach with difficulty. In the area 122, no heat exchange can be effected, so that the heat transmission area 116 for the vapor 104 to condense would decrease. As a consequence, the operating efficiency of the condenser 104 would decline significantly.
Therefore, a particular mechanism is required to discharge the non-condensing gas 121 accumulated within the condenser 100. Japanese Utility Model Publication No. SHO-63-47751 discloses a heat exchange apparatus for an automotive vehicle engine, which is designed to reduce a temperature difference between upwind and downwind portions of cooling air of the heat exchanger and control opening/closing of an electronic magnetic valve, provided in a tank beneath the heat exchanger, to discharge the non-condensing gas when the working medium has reached a high temperature. However, in the disclosed heat exchange apparatus, the opening/closing of the electronic magnetic valve is controlled on the basis of the temperature condition alone. Therefore, even vapor that can not be differentiated on the basis of the temperature condition would be undesirably discharged, and thus it was difficult to selectively discharge only the non-condensing gas accumulated in the lower are of the gaseous-phase portion 116.
For the foregoing reasons, there has been a great demand for an improved non-condensing gas discharge device of a condenser which can reliably separate the non-condensing gas, remaining within the condenser and impeding condensation of the vapor, from the vapor and thus selectively discharge only the non-condensing gas so that the gaseous-phase portion of the condenser is filled only with the vapor, to thereby achieve an enhanced condensing efficiency and permit efficient heat exchange on the entire heat transmitting surface of the gaseous-phase portion.